This renewal application seeks NICHD support for 6 first-year, 6 second-year, and 5 third-year positions in the Pediatric Scientist Development Program (PSDP), a career development pathway for pediatric fellows from which 156 physician-scientists have graduated since 1987. The objectives of the program remain unchanged since its inception: (a) to recruit pediatricians whose outstanding potential as scientists can be developed by senior research mentors and (b) to expand the cadre of superbly trained pediatric physician-scientists, who will catalyze cutting-edge discoveries in child health and lead the pediatric departments of the future. Research activities occur in basic, translational, or clinical investigation; in epidemiology and biostatistics; in health services research; or in any other discipline relevant to the NICHD mission. Unique aspects of the PSDP include its national scope for recruitment of fellows and mentors, its intensive focus on career development during fellowship, its supra- institutional governance under the aegis of the Association of Medical School Pediatric Department Chairs (AMSPDC), its emphasis on research environments outside departments of pediatrics, and its multifaceted approach to mentoring that encompasses scientific mentors, PSDP committees, and pediatric department chairs. A Steering Committee, meeting biannually, sets programmatic policy; a Selection Committee interviews PSDP candidates; and an independent Program Evaluation Committee measures the program's effectiveness in ensuring fellows' success. A centerpiece of the PSDP is the annual career development curriculum that convenes PSDP fellows, advisory committees, and all US and Canadian pediatric department chairs at the AMSPDC meeting. Currently, PSDP graduates occupy faculty positions in more than 60 pediatric departments and their affiliates across North America. PSDP graduates have served as PIs on more than 160 NIH R, P, U, and K awards, of which 42% are currently active. Since 1987, the person success rate for PSDP graduates who apply for NIH R01 funding is 51%. Graduates now serve as pediatric department chairs, HHMI investigators, institute leaders, and division directors. Over its 25-year history, the PSDP has implemented a national strategy to expand the boundaries of child health research, to develop the research careers of rigorously trained pediatric physician- scientists, and to produce the next generation of investigative leaders in pediatrics.